Multipotential hematopoietic stem cells in the bone marrow

It has been generally held that human hematopoietic stem cells are lineage-negative CD34⁺ CD38^?. However, murine hematopoietic stem cells were reported to be CD34^?. We have characterized the surface phenotypes of murine hematopoietic stem cells by using a murine transplantation model. Our studies revealed that the majority of the stem cells in normal adult mice are CD34^? while a minority (15%–20%) being CD34⁺. Our studies also revealed that stem cells that are activated by injection of 5-fluorouracil in vivo, exposure to cytokines in vitro, or mobilization by G-CSF are CD34⁺ and that CD34 expression is reversible. It has been reported that fetal murine hematopoietic stem cells are CD34⁺. Our studies revealed that stem cells of juvenile mice are CD34+ and that the developmental change from CD34⁺ to CD34^? state takes place between 7 and 10 weeks of age. In adult mice, expression of CD38 by steady-state and activated stem cells was completely reciprocal of CD34 expression. Activated stem cells and the minority population of the stem cells in the normal mice are CD34⁺ CD38^?. In contrast, the majority of stem cells in normal adult mice are CD34- CD38+. Recently, we studied CD38 expression by stem cells of neonatal and juvenile mice. Stem cells of newborn mice are CD38^?. About half of the stem cells of 5-week-old mice are CD38⁺. Finally, our studies indicated that some of the CD34⁺ stem cells in the bone marrow of normal adult mice express lineage markers such as Mac-1 and CD4. These studies in a murine model clearly documented that expression of both CD34 and CD38 by stem cells is under developmental control and may be subject to changes induced by activation of the stem cells. In order to test whether or not these principles apply to human stem cells we tested surface phenotypes of human stem cells using two xenotransplantation techniques. Studies based on human/sheep xenograft model indicated that a significant portion of adult human long-term engrafting cells are CD34^?. Similar to mouse stem cells expression of CD34 by human stem cells was reversible. Studies based on our newborn NOD/SCID/β-microglobulin^null mice indicated that human cord blood stem cells are CD34⁺ CD38^?. These results appear to support the validity of studies of murine stem cells to provide insight into human stem cells.     

Senescence of hematopoietic stem cells and bone marrow failure

Functional failure in hematopoietic stem cells (HSCs) may bring fatal consequences because HSCs are the ultimate source of mature blood cells, which need continuous replenishment. One potential cause of HSC dysfunction is senescence, in which HSCs and progenitor cells enter a state of proliferative arrest. HSC senescence is genetically regulated and one particular regulator is the telomerase gene. Mutations in the telomerase gene complex have been found in patients with bone marrow failure syndromes. During a normal lifetime, HSC clones function over the long term and may not show any functional loss under normal circumstances. However, pathologic environments may limit HSC proliferation, accelerate HSC turnover, and shorten the functional life of HSCs, leading to HSC clonal exhaustion and senescence.     

骨髓造血干细胞与肝再生的相关性研究

感染、中毒等引起的急慢性肝损伤治疗是临床医学领域的世界性难题,干细胞的研究为肝再生提供了全新的思路.肝再生的细胞学机制涉及肝细胞、肝干细胞和骨髓干细胞等. 新近发现骨髓造血干细胞具有向肝细胞转化的潜能,可以在体内外被诱导分化为肝样细胞,移植到肝损伤动物体内可以修复肝组织损伤,这为肝再生研究开辟了新的途径.对骨髓造血干细胞参与肝细胞再生的深入研究,有可能找到肝损伤治疗的有效措施.     

In vivo radiosensitivity and recovery pattern of the hematopoietic precursor cells and stem cells in mouse bone marrow

Survival curves were determined for colony-forming hematopoietic stem cells (CFU-Mix and CFU-S10) as well as precursor cells (CFU-E, CFU-C, CFU-F, and BFU-E) in bone marrow of the mouse at various times up to 4 weeks after whole-body irradiation (1.5 or 3.0 Gy) in order to elucidate in vivo radiosensitivity and recovery patterns. These measurements represented the first attempts to examine CFU-Mix simultaneously with the other cell populations. CFU-E (D0 = 53 rad) and BFU-E (D0 = 68 rad) were the most radiosensitive. CFU-S10 (D0 = 81 rad) had intermediate radiosensitivity. CFU-Mix (D0 = 144 rad) and CFU-C (D0 = 157 rad) were relatively radioresistant. CFU-F (D0 = 257 rad) was the most radioresistant. The precursor and stem cells could be classified into three groups based on the recovery pattern. The first group, consisting of CFU-Mix, BFU-E, and CFU-S10, showed very slow recovery and did not reach normal levels even after day 28. CFU-E, the second group, showed the most severe depletion immediately after irradiation, and recovered most quickly with an overshoot at day 5. CFU-C and CFU-F cells, forming the third group, decreased more gradually and slightly, and recovered to the normal level after a transient rise by day 10-14.     

JAM-B regulates maintenance of hematopoietic stem cells in the bone marrow

In adult mammals, hematopoietic stem cells (HSCs) reside in the bone marrow (BM) and are maintained in a quiescent and undifferentiated state through adhesive interactions with specialized microenvironmental niches. Although junctional adhesion molecule-C (JAM-C) is expressed by HSCs, its function in adult hematopoiesis remains elusive. Here, we show that HSCs adhere to JAM-B expressed by BM stromal cells in a JAM-C dependent manner. The interaction regulates the interplay between HSCs and BM stromal cells as illustrated by the decreased pool of quiescent HSCs observed in jam-b deficient mice. We further show that this is probably because of alterations of BM stromal compartments and changes in SDF-1α BM content in jam-b(-/-) mice, suggesting that JAM-B is an active player in the maintenance of the BM stromal microenvironment.     

Bystander destruction of hematopoietic progenitor and stem cells in a mouse model of infusion-induced bone marrow failure

Infusion of parental lymph node (LN) cells into sublethally irradiated hybrid F1 recipients created a murine model for bone marrow (BM) failure. Affected animals developed fatal pancytopenia within 2 to 3 weeks, accompanied by BM oligoclonal T-cell infiltration and severe marrow hypoplasia indicated by approximately 10-fold declines in total BM cellularity, 15-fold declines in BM Lin(-)Sca1(+)c-Kit(+) cells, 100-fold declines in spleen colony-forming units, and 100-fold declines in hematopoietic progenitor and stem cells as estimated by irradiation protection in vivo. LN cells of both H2(b/b) and H2(d/d) haplotypes were effectors. Serum interferon-gamma (IFN-gamma) concentration increased 2- to 3-fold. Marrow cells were severely apoptotic, with high proportions of Fas(+) and annexin V(+) cells. Cotransplantation of 5 x 10(5) BM cells from clinically affected donors and 10(6) BM cells from H2 identical healthy mice could not rescue lethally irradiated recipients. Recipients had significantly lower cellularity in peripheral blood and BM, and cell mixtures failed to produce a stromal feeder layer to support marrow cell growth in vitro. Pathogenic T cells from donors after BM failure appeared capable of destroying hematopoietic progenitor, stem, and stromal cells from fully compatible healthy donors as "innocent bystanders." This effect can be partially abrogated by anti-IFN-gamma antibody.     

Production of hematopoietic stem cell-chemotactic factor by bone marrow stromal cells

Chemotactic factors produced by stromal cells in the bone marrow are characterized. Two kinds of factors produced by stromal cell lines are identified using blind-well Boyden's Chambers; one is a neutrophil- chemotactic factor and the other a hematopoietic stem cell (HSC)- chemotactic factor. The latter attracts blastic cells in a low-density fraction, which are Thy1lo, wheat germ agglutinin (WGA)hi, H-2Khi, Ly-1- , Ly-2-, L3T4-, Ly5-, and slg-. The molecular weight of this HSC- chemotactic factor is estimated to be more than 200 kD. Putative cytokines and growth factors, such as granulocyte colony-stimulating factor (CSF), macrophage CSF, granulocyte-macrophage CSF, stem cell factor (SCF), interleukin (IL)-6, and IL-3, do not possess HSC- chemotactic activity. These findings strongly suggest that bone marrow stromal cells produce a new factor that attracts HSCs.     

Culture of hematopoietic stem cells purified from murine bone marrow.

The results of the Y-chromosome in situ hybridization experiments, the MRA assessment, and the long-term production of CFU-GM in vitro indicate that our protocol to sort low density WGA+, 15/1.1-, Rh123 dull cells enriches about 200-fold for PHSC. Assays for spleen colony formation (CFU-S) and radioprotection (30-day survival) were shown to be unspecific for PHSC, and, therefore, we lack a quantitative PHSC assay. The absolute number of PHSC in the bone marrow is not known any more, the purity of our sorted population likewise is unknown. Long-term repopulating cells (PHSC) could be separated from short-term repopulating ones by using Rh123 staining. The short-term repopulating cells (Rh123 bright) provided sufficient offspring to protect lethally irradiated mice until endogenous PHSC could reconstitute hematopoiesis. These cells are therefore of interest for bone marrow transplantation, because they provide radioprotection without long-term repopulation and graft-versus-host disease. For gene therapy these cells are of limited use, and PHSC with extensive replication are needed. The PHSC were not cultured successfully. Less than 15% of the sorted Rh123 dull cells responded in semisolid or liquid cultures in the presence of growth factors. Proliferation without differentiation was not observed. This may indicate that the right growth factor has not been found yet. On the other hand, about 30% of the cells responded in stromal layers of long-term bone marrow cultures and prolonged CFU-GM production and cobblestone area formation were observed there, suggesting that cell-cell contact and adherence molecules play a regulatory role in PHSC replication.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of engraftable hematopoietic stem cells in murine long-term bone marrow cultures

OBJECTIVE: Long-term bone marrow cultures (LTBMC) are a potential source of hematopoietic stem cells (HSC) for transplantation. Previous reports indicate that feeding LTBMCs induces hematopoietic progenitor cycling, and other studies link HSC cycle phase with engraftability. Our study was initiated to further characterize LTBMC engraftability and determine if a cycle phase-related engraftment defect affects HSC from LTBMCs. MATERIALS AND METHODS: Competitive repopulation of lethally irradiated BALB/c females was used to examine engraftability of LTBMCs under "fed" or "unfed" conditions at 3 to 5 weeks culture. Tritiated thymidine suicide was used to determine the cycle status of HPP-CFC and CFU-S from LTBMCs. RESULTS: Total cell number in LTBMCs decreases from input. Quantitatively, both fed and unfed 3-, 4-, or 5-week cultures compete strongly with fresh marrow for 2 and 8 weeks, but not 6 months, after transplantation. Short-term engraftable HSCs expand between 3 and 5 weeks of culture. Clonal assays indicate no peak in S-phase of CFU-S at 24 and 48 hours after feeding, and fluctuation in both content and cycle status of HPP-CFC after feeding. CONCLUSIONS: Our LTBMCs engraft in all conditions, and the level of engraftment capability does not correlate with cell-cycle phase of CFU-S or HPP-CFC, or with time from feeding. Although the total cell number decreases from input, the proportion of short- and intermediate-term engrafting HSC in whole LTBMCs approximates that of fresh marrow and expands from 3 to 5 weeks in culture, whereas long-term engraftable HSCs are decreased in culture.     

Distinct B-cell lineage commitment distinguishes adult bone marrow hematopoietic stem cells

The question of whether a single hematopoietic stem cell (HSC) gives rise to all of the B-cell subsets [B-1a, B-1b, B-2, and marginal zone (MZ) B cells] in the mouse has been discussed for many years without resolution. Studies here finally demonstrate that individual HSCs sorted from adult bone marrow and transferred to lethally irradiated recipients clearly give rise to B-2, MZ B, and B-1b, but does not detectably reconstitute B-1a cells. These findings place B-2, MZ, and B-1b in a single adult developmental lineage and place B-1a in a separate lineage derived from HSCs that are rare or missing in adults. We discuss these findings with respect to known developmental heterogeneity in other HSC-derived lymphoid, myeloid, and erythroid lineages, and how HSC developmental heterogeneity conforms to the layered model of the evolution of the immune system that we proposed some years ago. In addition, of importance to contemporary medicine, we consider the implications that HSC developmental heterogeneity may have for selecting HSC sources for human transplantation.     

Developmental switch of mouse hematopoietic stem cells from fetal to adult type occurs in bone marrow after birth

Hematopoiesis originated by hematopoietic stem cells (HSCs) is distinguishable between fetal and adult mice. However, it is not clear whether the altered mode of differentiation is due to the change of properties of HSCs or different microenvironments in fetuses and adults. Here we show that fetal HSCs are fully capable of giving rise to all classes of B cells in the adult microenvironment. HSCs that are derived from fetal liver but not adult bone marrow (BM) of IL-7 receptor alpha chain (IL-7Ralpha)-deficient mice can also differentiate into B cells, suggesting that both IL-7 and thymic stromal-derived lymphopoietin (TSLP) are dispensable for fetal B cell development, because IL-7Ralpha is commonly used as a subunit of functional receptor complexes for IL-7 and TSLP. Similar IL-7/TSLP independent B cell potential is maintained by BM HSCs until 1 week after birth. In contrast, BM HSCs in mice older than 2 weeks of age absolutely requires IL-7Ralpha for B lymphopoiesis. These results demonstrate that fetal HSCs acquired adult characteristics between 1 and 2 weeks after birth in mouse BM.     

Distribution of hematopoietic stem cells in the bone marrow according to regional hypoxia

The interaction of stem cells with their bone marrow microenvironment is a critical process in maintaining normal hematopoiesis. We applied an approach to resolve the spatial organization that underlies these interactions by evaluating the distribution of hematopoietic cell subsets along an in vivo Hoechst 33342 (Ho) dye perfusion gradient. Cells isolated from different bone marrow regions according to Ho fluorescence intensity contained the highest concentration of hematopoietic stem cell (HSC) activity in the lowest end of the Ho gradient (i.e., in the regions reflecting diminished perfusion). Consistent with the ability of Ho perfusion to simulate the level of oxygenation, bone marrow fractions separately enriched for HSCs were found to be the most positive for the binding of the hypoxic marker pimonidazole. Moreover, the in vivo administration of the hypoxic cytotoxic agent tirapazamine exhibited selective toxicity to the primitive stem cell subset. These data collectively indicate that HSCs and the supporting cells of the stem cell niche are predominantly located at the lowest end of an oxygen gradient in the bone marrow with the implication that regionally defined hypoxia plays a fundamental role in regulating stem cell function.     

Fractionation of mouse bone marrow by adherence separates primitive hematopoietic stem cells from in vitro colony-forming cells and spleen colony-forming cells.

Fractionation of mouse bone marrow by adherence to tissue culture plastic was used to characterize the adhesive properties of hematopoietic stem (HS) cells capable of long-term reconstitution. The adherent fraction that represents approximately 13% of the total marrow population was virtually devoid of in vitro colony-forming cells and spleen colony-forming cells but did contain approximately 30% of the total HS cells recovered from the procedure. These cells could be detected by both the competitive repopulation assay and by repopulation of W/Wv recipients. In approximately 60% of the recipients from the competitive repopulation experiments, the contribution of the adherent marrow cells was relatively low early (8 to 10 weeks) after transplantation. With time, however, the hematopoietic contribution from these cells increased, reaching a stable level 20 to 30 weeks posttransplantation. In the remaining recipients (40%), the contribution from adherent cells was already significant within 8 to 10 weeks of transplantation and did not change dramatically throughout the course of the experiment. Adherent bone marrow containing significant numbers of HS cells was unable to protect mice from radiation death, indicating that these early cells in the absence of later-stage progenitors are unable to provide this function.     

小鼠骨髓造血干细胞转化为肝细胞的实验研究

为进一步明确向肝细胞分化的细胞为骨髓中的那一亚群细胞,我们将纯化后的雄性小鼠造血干细胞移植到雌性受体小鼠的体内,然后在受体小鼠的肝脏内进行检测,以确定有无供体来源的肝细胞存在。一、材料与方法1.实验动物、主要器材和试剂:健康清洁级雌雄性纯系BALB/C鼠,8～12周龄,均由第一军医大学动物实验中心提供。主要试剂及材料:磁性活化细胞分选(magnetic activated cell sorting,MACS)分离用MiniMACS缓冲液,     

体外诱导小鼠骨髓间充质干细胞分化为肝样细胞

目的:体外诱导小鼠骨髓间充质干细胞分化(BMSCs)为肝样细胞,提高分化效率.方法:将第一代BMSCs随机分为诱导组和对照组.诱导组加肝细胞生长因子、成纤维生长因子、表皮生长因子、抑瘤素M等进行诱导培养,观察细胞形态,检测甲胎蛋白(AFP)、白蛋白(A1b)、细胞角蛋白18(CK18)、酪氨酸氨基转移酶(TAT)和细胞色素P450 2b9(CYP2b9)的mRNA表达,A1b合成以及A1b和CK18蛋白标记细胞阳性率.结果:诱导组第3天出现多边形细胞,5—7d上皮样细胞呈岛状分布,14 d呈铺路石状.对照组细胞为长梭形.第7,14,21天,诱导组细胞AFP,A1b,CK18 mRNA和A1b蛋白检测阳性;第14,21天,细胞表达TAT和CYP2b9 mRNA.对照组除AFP mRNA呈弱阳性外,其余均为阴性.第7,14,21天,诱导组CK18阳性率分别为71.4%.75.9%,80.6%:A1b阳性率分别为75.0%,79.7%.81.1%.而对照组第7天CK18和A1b阳性率仅2.3%,1.7%,与诱导组相比有显著差异(P_(CK18)=1.97×10~(-5),P_(A11b)=3.08×10~(-6)).结论:BMSCs在体外可以被诱导分化为肝样细胞,诱导率最高可达80%以上.     

Changes in hematopoietic stem cells in bone marrow of mice with Plasmodium berghei malaria

An impaired erythropoietic response to anemia has been noted in human patients with malaria and in rodents experimentally infected with Plasmodium berghei. We have attempted to characterize the erythropoietic response in mice with a fatal P berghei infection, with particular emphasis on changes in marrow hematopoietic stem cells. Mice infected with P berghei had dramatic decreases in bone marrow cellularity, erythroblasts, BFU-E, and CFU-E as early as 24 hours postinfection and before there was any change in hematocrit. With development of anemia, marrows became erythropoietic with some expansion of the CFU-E compartment, but the BFU-E pool remained depleted and reticulocyte response was inadequate. There was no significant change in CFU-S from marrows of malaria-infected mice one day after infection. The lethality of malaria infection may take three weeks to be revealed, but it may be determined within hours of the infection by the irreparable changes in marrow erythroid stem cells.     

Wnt-inhibitory factor 1 dysregulation of the bone marrow niche exhausts hematopoietic stem cells

The role of Wnt signaling in hematopoietic stem cell fate decisions remains controversial. We elected to dysregulate Wnt signaling from the perspective of the stem cell niche by expressing the pan Wnt inhibitor, Wnt inhibitory factor 1 (Wif1), specifically in osteoblasts. Here we report that osteoblastic Wif1 overexpression disrupts stem cell quiescence, leading to a loss of self-renewal potential. Primitive stem and progenitor populations were more proliferative and elevated in bone marrow and spleen, manifesting an impaired ability to maintain a self-renewing stem cell pool. Exhaustion of the stem cell pool was apparent only in the context of systemic stress by chemotherapy or transplantation of wild-type stem cells into irradiated Wif1 hosts. Paradoxically this is mediated, at least in part, by an autocrine induction of canonical Wnt signaling in stem cells on sequestration of Wnts in the environment. Additional signaling pathways are dysregulated in this model, primarily activated Sonic Hedgehog signaling in stem cells as a result of Wif1-induced osteoblastic expression of Sonic Hedgehog. We find that dysregulation of the stem cell niche by overexpression of an individual component impacts other unanticipated regulatory pathways in a combinatorial manner, ultimately disrupting niche mediated stem cell fate decisions.